1. Field of the Invention
The present invention relates to a graphics display device which displays graphics on a display device by means of a micro-computer and a graphics display method thereof and, more particularly, to a graphics display device suitable for such a system as a game machine which displays a plurality of graphics in motion at high speed, while three-dimensionally overlapping them with each other, and a graphics display method thereof.
2. Description of the Related Art
In recent years, in line with complication and advancement of the contents of games on game machines and dramatic presentation of virtual experiences in various kinds of presentations, there is a demand for various kinds of special functions appealing to perception of game players and viewers more effectively on display images of a graphics display device of this kind. One of such special functions is stereoscopic display. Here, stereoscopic display is referred to as a representation method in which graphics (sprite) in the foreground including a plurality of human characters move and overlap with each other at a high-speed on a three-dimensional scene having a depth to forward a game or a presentation.
In stereoscopic display of this kind realized by a conventional graphics display device, when a plurality of sprite graphics overlap with each other to an extent exceeding a predetermined overdrawing capacity, graphics located in the foreground which correspond to the amount of an overflow from the drawing capacity are not displayed, resulting in making display unnatural, depending on constitution of a scene.
FIG. 7 shows an example of structure of a conventional graphics display device. A conventional graphics display device 30 shown in FIG. 7 includes a drawing processing unit 31 for generating and outputting graphic data, a line buffer unit 33 for accumulating and outputting one line of graphic data output from the drawing processing unit 31, and a timing generation unit 32 for controlling operation timing of the drawing processing unit 31 and the line buffer unit 33. The drawing processing unit 31, having a built-in graphics ROM which stores original data of display graphics, conducts predetermined drawing processing in response to a clock signal CK and a drawing processing control signal CI output from the timing generation unit 32 to output graphic data composed of a display pixel data signal PD, a write enable signal WE to the line buffer unit 33, and an address signal LA indicative of an address of a storage position at the line buffer unit 33. The timing generation unit 32 receives input of the clock signal CK, and a vertical synchronizing signal V and a horizontal synchronizing signal H to output a drawing processing control signal CI for controlling the operation timing of the drawing processing unit 31 and a line buffer control signal LC for controlling the operation timing of the line buffer 33. The line buffer unit 33 temporarily stores graphic data (PD, WE, LA) output from the drawing processing unit 31 in response to the clock signal CK and the line buffer control signal LC output from the timing generation unit 32.
With reference to FIGS. 7, 8 and 9, description will be next made of operation of the conventional graphics display device for displaying a k-th line of graphics. FIG. 8 is a time chart showing each of signal waveforms and FIG. 9 is a diagram showing an example of display of the graphics. In this operation example, graphics G1 and G2 are displayed, with the graphics G1 displayed in the foreground (that is, with a higher display priority) as shown in FIG. 9.
First, the graphics display device 30 is supplied with the vertical synchronizing signal V from a host device (not shown) to initialize the timing generation unit 32. Next, the timing generation unit 32 is supplied with the horizontal synchronizing signal H from the host device once to responsively output the drawing processing control signal CI and the line buffer control signal LC. The drawing processing unit 31 is initialized in response to the drawing processing control signal CI and the line buffer unit 33 is initialized in response to the line buffer control signal LC to enter a drawing starting state.
Upon entering the drawing starting state, the drawing processing unit 31, for first displaying the graphics G2 whose display priority is low, serially outputs the address signal LA="40.about.47(h)" and the corresponding display pixel data signal PD as a pixel data value for drawing the graphics G2 in response to each clock signal CK. During this period, the value of the write enable signal WE assumes "0(h)", so that the pixel data of the graphics G2 is stored in the line buffer unit 33. Next, the drawing processing unit 31, for displaying the graphics G1 whose display priority is high, serially outputs the address signal LA="45.about.4C(h)" and the corresponding display pixel data signal PD as a pixel data value for drawing the graphics G1 in response to each clock signal CK. During this period, the value of the write enable signal WE assumes "0(h)", so that the pixel data of the graphics G1 is stored in the line buffer unit 33.
After the one line of pixel data including the graphics G1 and G2 is thus stored in the line buffer unit 33, the pixel data is output to draw each display line of a screen in question on the display device as shown in FIG. 9.
As described in the foregoing, for the stereoscopic display in which a plurality of graphics (sprite graphics) are displayed to have a positional relationship in the depth direction, conventional graphics display devices draw graphics while overlapping them from the back of the screen toward the foreground in order. Then, when the plurality of sprite graphics overlap with each other to an extent exceeding a drawing capacity of the graphics display device, graphics located in the foreground which exceed the drawing capacity are not displayed.
FIGS. 10 and 11 are diagrams showing examples of stereoscopic display in which five graphics G3 to G7 are disposed in order from the foreground toward the back of the screen. FIGS. 10(A) and 11(A) show a positional relationship among the displayed graphics in the depth direction, while FIGS. 10(B) and 11(B) show a state of the actual display. With reference to FIG. 10, the graphics G7 is completely hidden by other graphics, and therefore the four graphics G3 to G6 are displayed in FIG. 10(B). On the other hand, with reference to FIG. 11, the graphics G3 is not displayed because display of the graphics exceeds the drawing capacity of the graphics display device. As a result, each part of the graphics G4, G5 and G7 is exposed which would be hidden by the graphics G3 in FIG. 11(B). In a case where the graphics G3 is a main element of the display scene, such missing of graphics as illustrated in FIG. 11 stands out to make the screen unnatural.
As described in the foregoing, conventional graphics display devices and graphics display methods thereof have a drawback that since in stereoscopic display where a plurality of graphics are displayed overlapping with each other in the depth direction, the graphics are overlapped in order from the back toward the foreground, when graphics display is made exceeding a drawing capacity, graphics located in the foreground will not be displayed and in some cases the missing graphics stands out very much to make the screen unnatural.